Control mechanism responsive to a recorded signal



April 2, 1957 A. FLAN ETAL CONTROL MECHANISM RESPONSIVE TO A RECORDEDSIGNAL Filed June 21, 1955 INVENTORS ANTHONY FLAN HAROLD M/LLER ATTORNEYplied to a speaker in the usual 'fashi'on.

age high resistance source.

id tates Patent Our invention relates to a control mechanism respons'iveto a control signal superimposed on the main signal recorded on atap'e.

it is frequently desirable to "provide "both the reproduction erseundsrecorded on 'a't'ap'e' andtlre performance of control functions'as thereproduction proceeds. Thus,

for example, it may be desirable to arrest operation 'of the reproducingmechanism at "theend of a'jplay-ba'ck, so that an unattended reproducer"will play 'a complete program and then'reverttoan'unenergizedconditio'n. In another application it may be necessaryto apply or interrupt the power supply to a remote apparatus, such asthe automatic slide changer'mechanism of a 's'lideprojector. In thisinstance it is necessary to interpose the control operations onthereproducing "operation "so that the listener observes no change in thesound program, although the projector changes from one slide to 'thenext.

In accordance withthe'presentinvention an apparatus is provided todotheseand similar-operations. 'Inbrief, the signal picked up from thetapeis amplified and ap- At a signal takeofi point located in advanceof'the volume control the composite signal is appliedto 'a frequencyselective amplifier which amplifies only the selected control frequency,say 25 cycles. fhe resultant selectively amplitied signal is applied toan integrating network for application to the control electrode of thecontrol tube,

that-electrode being normally has to low-space current flow conditionbynegative bias "taken from the low voltis maintained for a time-slifiicien't-tocharge theintegratingcircuit and drive the'c'ontrolelectrode of the control tube positively, the current flow increases tothe relay pickup value. Depending upon the selected condition of themechanism, the relay closes and seals in "or closes only so long as thecontrol signal ismaintained.

The selected condition of fthesystem isdetcrmined by the position of amulti=bank multi-pos'ition selector switch. In the manual position onebank-of this sw'itch 'c onnects the control electrode of the controltube to a point of positive "voltage through normally open relaycontacts, thus causing the relay to seal :in. The relay may subsequentlybe deenergized by grounding thepoint of positive voltage. Also, when theunit is in the manual position the solenoid provided to engage the .tapedrive mechanism is deenerg ized by reason of a set of normally closedcontrol relay contacts which areconnected to another bank on theselector switch, .thereby arresting further travel of the tape overthereproducing head.

When-the unit is set in the automaticposition,the selector switchinterrupts the relay sea1in circuit and additionally defines a solenoidenergizing circuit independent of relay pickup. Accordingly, the tapecontinues to wind-and the relay is only momentarilyenergized by thecontrol signal.

Provision is made for limiting the'response of the cont-rol .tube torandombursts of signal containingsubstantial control frequencycomponents. In par't'this response When the control voltage limitingaction is obtained from a time delay or integrating circuit.Additionally, negativefbias imposed on the control tube assures thatoperation will take .place only in the presence of a control signal ofsubstantial magnitude. During relay operation the negative 'bias on thecontrol tube is overcome by a source of positive voltage.

t is therefore a general object of the present invention to provide animproved control mechanism responsive to a control signal of non-audiblefrequency recorded on a tape.

A further object of the present invention is to provide a positiveacting control -system responsive to a relatively low frequency, suchas.25 cycles.

Still another object of the presen't invention is .to provide animproved control system responsive to a nonaudible control signal whichdoes not respond to signal bursts having substantial control frequencycomponents.

Yet another object of'the'present invention is to provide an improvedapparatus responsive to a control signal recorded on tape, whichapparatus positively .seals in and yet may be positively started fromthe seal-condition.

Still another object of the present invention is to provide an improvedapparatus responsive to control signal which may be selectively seteither to seal-in the triggered condition or, alternatively, tojremainin that condition only so long as control signal is present.

Additionally it is an object of the present invention to provide animproved highly flexible device adapted to reproduce the tsignal on atape .and at the same time .per'form controliunctions in response to acontrol signal of predetermined frequency on .the .tape, such devicebeing simple, reliable, inexpensive, gpositive acting, flexible, andreadilymanufactured to the end that a mechanism suitable fora widevariety of commercial advertising, lecturing and other purposes .isobtained.

The-novel features which we believe to be characteristic of ourinvention are .set forth with particularity in the appended claims. Ourinvention itself, however, both as to its organization and method ofoperation, together with further objects -and advantages thereof, willbest be understood by. reference to the following description taken inconjunction with the accompanying drawingsin which: Figure 1 is aschematic circuitdiagram of a controlled tape reproducer constructed inaccordance withthe present invention; and

Figure 2 is afragmentary diagrammatic top plan view of the mechanicalmechanism of .the unitoflFigure 1.

General "construction and operation The reproducer shown in Figure '1includes a Yourposition manual selector switch which has four banks ofcontacts indicated generally at 10a, 10b, Ilic and 10d. Each of thesehas a single contact arm movable selectively to one of each of fourfixed contacts. The arms are mechanically connected to 'be rotated inunison by means of a suitable knob. 'The four positions of the selectorswitch indicated at '1, 2, 3 and 4 at each set-of contacts on Figure 1are, respectively o standby, manual and automatic. In the bit positionselector switch bank 10d interrupts the supply of energizingrpower fromsource'28 to the complete unit. Accordingly, the capstan drive motor 92does not rotate; the amplifierpower transformer'84-is not energized; andthe pinch roller pull-in solenoid 12 does .not pull that roller totape-engaging position.

is not moved over the reproducing head even though capstan 16 isrotating. An amplifier muting circuit is defined by the selector switchbank 1012 so that extraneous and pickup noises are not reproduced in thespeaker 23.

When the selector switch is on manual, the pinch roller pull-in solenoid12 is energized through the normally closed contacts 22:: of the controlrelay 22 and bank 10c of the selector switch. When a control signalappears, the control relay 22 is energized to open these contacts andthereby deenergize solenoid 12. The control relay 22 seals-in by reasonof the action of normally open contacts 22b so that the pinch rollerpull-in solenoid 12 remains deenergized and the tape 18 comes to a stopuntil the unit is reset by momentary closing of the manual start switch24.

When the selector switch is in the automatic condition, the pinchrol'ler pull-in solenoid 12 is permanently.

energized through the number 4 contact of portion 10c of the selectorswitch. The tape 18 is accordingly in continuous movement irrespectiveof the condition of relay 22. With this setting a control signalenergizes relay 22 only while the control signal is present and for ashort time thereafter. At all other times the relay 22 is deenergized.

The normally closed contacts 220 of the control relay 22 control theapplication of power from source 28 to the female appliance socket 30.The socket receives an appliance plug to an automatic slide projector orother device desired to be controlled in response to the condition ofthe relay 22.

Construction The amplifier defined by vacuum tube 32 amplifies the a tothe second amplifier defined by vacuum tube 36. The

anode of tube 30 is connected back in a negative feedback circuit to thecathode of tube 32 through resistance 38 and capacitor 40 which serve asan equalizing network so that the signal appearing in the anode of tube36 is a, faithful reproduction of the sound initially recorded on tape18.

The signals at the anode of tube 36 are further ampified by vacuum tube42 and are applied through the network defined by capacitor 44,resistance 46 and potentiometer 48 to the power amplifier pentodeelectron tube 50. The potentiometer 48 serves as a volume control. Theanode-cathode space current of the tube 50 passes through the primarywinding 52a of the output transformer 52. The secondary winding 52!)feeds the alternating components of this current to the speaker 23 l ina proper impedance match to reproduce in audible form the signalsrecorded on tape 18.

The selector switch bank 10b defines a grounding circuit for the movablearm of potentiometer 48. This circuit is always effective in the number2 contact position and in the number 3 contact position is effectivethrough the normally open contacts 22d of relay 22.

Signals at the anode of tube 42 are also applied through capacitor 54and resistance 56 to the amplifier tube 58. The anode of tube 58 isconnected in negative feedback relation to the control electrode by thenetwork shown generally at 60. As is hereinafter described, this networkis characterized by a high impedance between the anode and the controlelectrode at the frequency of the control signals, such as 25 cycles.Accordingly, there is little or no negative feedback for such signalsand the full amplifier gain is available. As to all other signals,however, the network 60 provides a comparatively low impedance feedbackpath which reduces the amplification of tube 58 to a point wherein thesignals at its anode are too small to actuate the relay 22 ashereinafter described.

Output voltage from the tube 58 is taken through capacitor 62' andresistance 64. This voltage is rectified '4 by the rectifier 66 toprovide at the junction of resistance 64 and capacitor 62 a series ofhalf-wave rectified 25 cycle pulses when the control signal is presentand otherwise no substantial signal.

The filter defined by resistances 68 and 70 and capacitors 72 and 74serves as an integrating network to prevent short momentary signalsacross resistance 64 from reaching the control electrode of the relaycontrol tube 76.

The anode current of control tube 76 is passed through the relay winding22 as shown. This circuit may be traced from the cathode of rectifier 78through conductor 80 to the relay winding 22 and thence through theanodecathode space path of tube 76, and cathode resistance 82 back toground and to the center tap of the high voltage winding 84a of powertransformer 84.

The high voltage end of the control relay winding 22 is connected toground through the series resistances 86 and 87. The resistance 87 maybe short circuited by the manual start switch 24 to reduce the currentflow in tube 76 and causes relay 22 to drop out as hereinafterdescribed. The common connection of resistances 86 and 87 is alsoconnected through switch contacts 22b and contact 3 of the selectorswitch bank 10a to the control electrode of tube 76. Negative biasvoltage is also applied to the control electrode through resistance 88and half-wave rectifier 90, this voltage being taken from the heatersupply winding 84b of the transformer 84.

The capstan drive motor 92 is connected across the power supply source28 through the bank 10d of the selector switch. The source 28 is theusual 117 volt 60 cycle service supply.

The pinch roller 14, Figure 2, is mounted on and carried by the rockablearm 94 which is pivotally supported at 96 for swinging movements into orout of engagement with the capstan 16. The pinch roller engagingsolenoid plunger 12a is linked by link 100 to the swingable arm 94 sothat when the solenoid 12 is energized the plunger 12a is drawn into thesolenoid and the pinch roller 14 is pulled snug against capstan 16. Thepinch roller is constructed of rubber-like material to force the tape 18against the capstan 16 in effective gripping action. When the solenoidis not energized the pressure of the tape against the capstan requisitefor tape-driving engagement is not present and the tape is accordinglynot driven by the capstan 16.

The rectifier 102 and capacitor 104 serve to rectify the voltage ofsource 28. This rectified voltage appearing across capacitor 104 isapplied through normally closed contacts 221: of relay 22 and throughthe selector switch bank 100 to the solenoid 12a as shown.

In a unit constructed in accordance with the present invention and usingthe circuit shown in Figure 1, the component parts are as follows:

Resistance 32a 3.9 megohms. Resistance 32b 330 ohms. Resistance 32c470,000 ohms. Capacitors 40 and 44 470 micromicrofarads. Resistance 38680,000 ohms. Resistance 36a 470,000 ohms. Capacitor 36b 0.01microfarads. Resistance 42a 470,000 ohms. Resistance 42b 4700 ohms.Resistance 46 470,000 ohms. Potentiometer 48 250,000 ohms. Resistance50a 270 ohms. Capacitor 50b 20 microfarads. Capacitor 52c .005microfarads. Resistance 51 100,000 ohms. Capacitors 54, 60a, 62, 72 and74 0.1 microfarads. Resistances 56, 68 and 70 1 megohm. Capacitors 60band 60c .01 microfarads.

Resistance 60:: 680,000 ohms.

Resistance '64 greases Resistance 58a L. 1000 ohms.

- 1.;5 m'e'goh'tns. 1500 ohms. 6800 ohms. 100,000bhins.

Resistance 82 Resistance 87 Resistance '86 amperes; dro out 6 t0 7liiilliam- P' m- 300 volts 'DJ C.

Detail d operation The operation of the speaker enefg'iliing "systemextending from pickup head 20, through electron tubes 32, 36, 42 and 50is conventional. The current fiow in winding 52b is in accordance withthe recorded sound on the tape, thereby causing speaker 23 to reproducethose sounds. The volume of the sounds so reproduced is determined bythe position of the potentiometer 48. t

When the selector switch "is in the standby: position the movable arm ofbank b engages the axes contact 2. This grounds the movable arm ofpotentic'imete'r '48 to mute the speaker 23 since by this action no timevarying signal can reach "the speaker. When the selector switch is inthe manual position, the fiired contact 3 of bank 10b is engagedby theniovable arnither'e'of to form a muting circuit for "the control-'elec-trode of Normal voltage at conductor 80 tube 56 through thenormally open relay contacts 22d.

Accordingly, tube 50 and speaker 22ar'e muted when the unit is in manualposition and the relay is energized and at all other times the operationis normal.

The control signal is taken from the anode of tube 42 throughcapacitor'54'and resistance 56 to appear across the resistance 106. Thissignal isa composite signal including both the sound components of "therecorded signal and the control components, if present. is abovedescribed, the control component may be "a signal outside of the audiblerange. In practice, 25 cycle signals have been used for this purpose,although other frequencies may be used if desired.

The electron tube 58 serves to amplify selectively the composite signalacross resistance 106. At the selected control frequency, such as 25cycles, the feedback network '60 has comparatively high impedance. Thispermits the electron tube 58 to amplify with its normal and usualamplification. tube in the circuit shown, the amplification factor isabout 100 so that gain may be-of the 'order decibels for cycle signals.On the other hand, forsignals of substantially different frequency thecomparatively low impedance of the feedback network 60 provides'such alarge amount of negative feedback that the amplification of tube '58 issubstantially less than unity, so that such signals do not appear at theanode of tube 58. As a consequence, the signalsacross capacitor 62 andresistance 64 are of very low magnitudein comparison to the magnitudeofthe 25 cycle 'orotherselected control frequency.

The resistance 64 isshort circuited by the'rectifier 66. Accordinglyonly the positive half of each 25 cyclewave appears across thatresistance. Each such half wave charges capacitor 72 throughresistance68. Thisch arging circuit may be a'time-consta'nt of the order of second'so that a succession of 25 cycle pulsesis required. As the capacitor'72 charges it in turn charges capacitor 74 through resistance 70.Resistance 70 and capacitor For example, with a 12AX7 74 may be, forexample, /1 second time "constant, giving further integrating action andrequiring a still longer series of pulses before the voltage risessignificantly. The net effect is to produce across capacitor '74 a substantial voltage'only when the 25 cycle control signal is maintained fora substantial time period such as, for ex ample, /2 second.

The network defined by capacitors 72 and 74 and resistances 63 and .79serves to isolate the control electrode of tube 76 from momentary burstsof 25 cycle energy. This energy may occur, 'foreXample, by reason ofnormal variation in the recorded'sound, such as music. Since the tube 76is to be energized only by the desired sustained control signals, thenetwork serves the useful purpose of preventing the false operation thatmight otherwise take place.

The space path current fiow f'or tube 76 passes through the energizingWinding of relay :22. The current flow path may be traced from thecathode of rectifier 78 through conductor 8t) and winding 22 to theanode of tube 76. The cathode of tube 76 is connected through resistance82 to the ground and thence to the center tap of wind-ing 84a of powertransformer '84. The high voltage side of Winding 22 is connectedthrough i'esistances 86 and 88 to ground, thus defining a point ofintermediate potential at the junction of these resistances.

In the absence of control signal, the tube 76 is biased to a relaydropout current flow by reason of the negative bias obtained from powertransformer winding 84b. This is the heater current supply winding whichmay, for 'eX- ample, produce 6.3 voits "R. S. This voltage is appliedthrough half-wave rectifier 9b, resistance 88 and-the resistances 7b, 63and -64 to ground and thence to the grounded terminal of winding 84. Thecontrdl-electrode of tube "76 has accordingly about half of theavailable negative bias voltage. Capacitors 72 and 74 serve as filtercapacitors to hold the control electrode voltage of tube '76substantially constant during the time intervals between successivecycles of the 60 cy'ele voltage of Winding 8412. This negative biasvoltage, together with the biasing action of resistance 32, serves tomaintain the current flow in tube 76 below the relay dropout currentwhen thereis no signal at the controlelectrode of tube 76. When controlsignal is present a positive signal voltage is applied to the controlelectrode of tube'7ti thus swinging the control electrode in directionto increase the anode-cathode space-current. If the control signal is ofsufficient amplitude and duration this positive swing proceeds to avoltage value sufficient to cause cathode-anode current flow capable ofpicking up the relay 22. When the selector switch is in the number 3position, this relay thereupon seals in the energized state since thecontacts 2212 close to 'bring the control electrode of tube 76 to thepotential at the junction of resistances 86 and 88 which is, forexample, about 15 volts positive. Simultaneou sly, the bank 10b of theselector switch makes contact through the number 3'contact and thecontacts 22d to ground, thereby bringing the movable terminal ofpotentiometer 48 to ground potential and muting the speaker 23.Additionally, the bank ltic. of the selector switch makes contactthrough the number 3 contacts to the normally closed contacts 22a ofrelay 22 which, when energized, open contact. This removes theenergizing voltage from pinch roller engaging solenoid i2 and therebyreleases the arm 94, Figure 2. Without the solenoid pull on arm 94 thepinch roller 43 is not subjected to the pressure required to bring thetape 18 into driving 'engagement with the capstan.

v By the above described sequence of events, the control signal arrestsall further operation of the unit. At the same time, however, theunit isplaced in a standby condition with the capstan 1'6 turning and theamplifier circuits in the warmed up condition. When it is desired torestoreoperation, the manually operated-switch 24 is momentarily"closed. This reduces the control electrode of tube 76 to negativepotential through the bank a of selector switch 10 (now in the number 3position), the normally open contacts 22!) of relay 22, and the voltagedivider formed by resistance 89 (which connects to ground potential) andresistance 88 (which connects to the negative potential of rectifier90). Since at this time the control electrode of tube 76 is firmlybrought to negative potential, the relay 22 positively drops out.

When the selector switch banks 10a, 10b and 100 are in the number 4position the seal-in circuit for relay 22 through the normally opencontacts 22b is ineffective since it is open at contact number 4 of therelay bank 10a, Consequently, the relay 22 is closed only when a controlsignal voltage is applied to the tube 76 and it opens as soon as thepositive control signal voltage disappears at the control electrode ofthat tube. Moreover, the solenoid 12 is under this condition energizeddirectly through the number 4 contact of relay bank 10c independently ofthe condition of relay 22. As a consequence the solenoid 12 remainsenergized despite the presence of con trol signal and the pinch roller14 is held against capstan 16 to maintain the forward movement of thetape 18. The induced signal in the head 20 accordingly continues. Itwill be observed that in the number 4 position of selector switch, thebank 10b defines an open circuit so that closure of the relay contacts22d gives rise to no muting effects.

When the selector switch is in the number 2 position, the pinch roller14 is not subject to pressure due to the solenoid 12 and the tape 18 isaccordingly not moved. This results from the fact that the number 2selector switch contact in bank 10c is not connected to a source ofsolenoid operating energy.

It will be noted that the normally closed relay contacts 220 supplypower to the female appliance socket 3%. This socket may, for example,receive a mating plug to energize a slide projector mechanism of thetype which advances a new slide to position whenever power ismomentarily interrupted. With this arrangement the control signal on thetape 18 momentarily deenergizes the socket when the unit is in theautomatic position. This is desirable, for example, where the tape 18includes a narrative which is illustrated by a sequence of slides, forthe narrative continues uninterrupted while the slides are changedautomatically atthe desired times. If desired, contacts 22c may be ofthe normally open type, in which event the socket 30 is energized whencontrol signal is present. Alternatively, additional contacts may beprovided on the relay 22 to perform switching operations if desired.

When the unit is adjusted to the manual condition the tape 18 may, forexample, be a continuous loop tape and the signal recorded at the end ofeach complete rendition. The manually operated switch 24 may in thisinstance be a push button to be actuated by the listener desiring tohear one complete cycle of the program. Alternatively, switch 24 may beautomatically operated, as by a photo-electric system, so that when apatron interrupts a light beam the program is automatically initiated.It will be noted that in this connection the closure of switch 24produces no sound at the speaker 22 since the speaker is muted and doesnot otherwise interrupt operation of the unit.

In the above description the bank 10d is shown on the selector switch todeenergize the unit when the switch is in the number 1 position.Alternatively, the switch may have a on-otf switch which is actuated toon position by shaft rotation prior to the time switch positions 2, 3and 4 are reached.

It will be noted that the resistance 88 defines a high impedance biasvoltage source to the control electrode of tube 76. Because of thisimpedance, the signal voltage coming from tube 58 to the capacitorfit-which itself has in efiect a rather high internal impedance-iscapable of varying the control electrode voltage of tube 76.

In the actual construction described above the no-signal voltage at thecontrol electrode of tube 76 may range from about 2 to 5 or more voltsnegative; the voltage in the presence of signal was about 12 voltspositive; and the voltage at seal-in with the selector switch at themanual position was about 12 volts positive. All of these voltages mayvary within wide limits. Indeed, this is one of the advantages of theapparatus of the present in vention, which operates positively andeffectively over wide variations in the components and conditions ofoperation. This not only permits a less expensive construction but inaddition makes the control operation more positive. Under this operationthe tube 86 draws about 3 milliamperes in the normal state and in thepresence of control signal or the seal-in it draws about 10milliamperes.

The capacitor 104 has a relatively large capacitance, such asmicrofarads. This delays the release of the solenoid 12 for apredetermined time period after the operation of switch 22a wouldotherwise release that solenoid. This operation additionally serves tomake the unit operate in a positive fashion since there is otherwise achance that the tape 18 will come to rest at a point where the controlsignal is still on the tape. If this happens the momentary closure ofswitch 24 will only start the unit which will immediately stop becauseof the control signal on the tape. The delaying action of capacitor 104causes the tape to continue its motion after the first actuation ofrelay 22 so that the portion bearing the control signal (for example, athree inch length) completely clears the head 20.

In operation, the current flow from rectifier 102 charges the capacitor104 prior to and while the solenoid 12 is picking up. So long as thesolenoid 12 remains energized this charge remains on the capacitor. Whenswitch 22a opens (or switch 10 is reset) the capacitor 194 dischargesthrough solenoid 12, which gradually exerts less and less force on thearm 94 and pinch roller 14 until the force falls to negliglibletape-releasing value, at which time the tape stops.

While we have shown and described a specific embodiment of the presentinvention it will, of course, be understood that numerous modificationsand alternative constructions may be made without departing from thetrue spirit and scope thereof. We therefore intend by the appendedclaims to cover all such modifications and alternative constructions asfall Within their true spirit and scope.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A reproducing and control device operable to reproduce the audiblesignal on a recording and to perform control operations in accord withcontrol signals of predetermined frequency on the tape, the devicecomprising: a pickup head; means operable when energized to draw thetape over the head; a sound amplifier adapted to re produce signalspicked up in the head; a speaker responsive to the amplifier output; acontrol signal amplifier connected to the sound amplifier at apredetermined point and including frequency selective elements operableto suppress signals of frequency other than control frequency; mean torectify the output of the control signal amplifier; a resistor andcapacitor connected across said last means to define an integratingcircuit; an electron tube havinga cathode, anode, and control electrode;means to supply cathode-anode space voltage to the said tube; relaymeans responsive to the cathode-anode space current of said tube, saidrelay means having at least two sets of normally open contacts and oneset of normally closed contacts; a selector switch having at least threebanks and three sets of contacts; means including one of said selectorswitch bank in one selector switch position to connect the controlelectrode of the tube through one set of normally open relay contacts toa point of positive potential, whereby the relay seals in upon actuationat said one selector switch position; means including another of saidselector switch banks in said one selector switch position to connect apoint in said amplifier after said first mentioned point to ground,whereby the sound amplifier is muted upon relay actuation at said oneselector switch position; and means to energize said first means througha third Selector switch bank and the normally closed relay contacts whenthe selector switch is in said one position and directly through thesaid third selector switch bank when the selector switch is in anotherposition.

2. A control mechanism for use with a tape reproducer having a drivemechanism operable when energized from a voltage source to drive thetape over a reproducing head, the control mechanism being responsive toa non-audible signal recorded on the tape and selectively operable toassume a quiescent state either permanently or momentarily when acontrol signal appears, the mechanism comprising: an electron tubehaving cathode, anode and control electrodes; a relay having normallyclosed and normally open contacts and an actuating winding; a source ofunidirectional voltage; means connecting said source to theanode-cathode space path of said tube through the actuating winding ofthe relay; means to apply the control signal in positive sense to thecontrol electrode; resistance means operable to apply predeterminednegative bias voltage to the tube, whereby the relay remains open in thenormal state and picks up when the control signal is applied to saidtube; a selector switch having at least two banks and at least twopositions on each bank; means connecting the control electrode of saidtube to said unidirectional voltage source through one set of contactsof one bank of said selector switch and in series with the normally openrelay contacts and a resistance; means operable to energize said drivemechanism through the corresponding contacts of the other bank of theselector switch and the normally closed relay contacts; means directlyconnecting said drive mechanism to said last means directly throughother contacts of the said other bank of the selector switch; and meansselectively operable to connect said last-mentioned resistance toground.

3. A control system responsive to a periodic sub-audible comparativelylong control signal superimposed on a main signal having signal burstscontaining control frequency components, the system comprising:frequency selective means operable to pass the control signal whilerejecting signals of other frequencies; means to rectify the output ofsaid first means; integrating means responsive to the output of saidsecond means; an electron tube having a cathode, anode and controlelectrode; means to apply the output of said integrating means to thecontrol electrodecathode space path of the tube; biasing means havingsubstantial effective internal resistance operable to bias the controlelectrode in the negative sense in relation to the cathode whereby inthe normal condition the tube has a predetermined small cathode-anodespace current; means to apply positive anode-cathode space path voltageto the said tube; relay means responsive to the anode-cathode space pathcurrent of said tube and operable when energized by predetermined largecurrent to apply a positive potential to the control electrode of thetube, thereby scaling in the energized condition and overcoming thebiasing means; and means selectively operable to destroy said positivepotential to bring the control electrode to cathode potential and causethe relay means to drop out.

4. A control system responsive to a periodic sub-audible comparativelylong control signal superimposed on a main signal having signal burstscontaining control frequency components, the system comprising:frequency selective means operable to pass the control signal whilerejecting signals of other frequencies; means to rectify the output ofsaid first means; a capacitor and resistance in series across said lastmeans to define an integrating circuit; a source of alternating E. M.F.; means connecting said source through a half-wave rectifier and aresistance to charge said capacitor in sense opposite to the charge ofthe control signals; an electron tube having cathode, anode, and controlelectrodes; means connecting the cathode and control electrode of saidtube across said capacitor so that the control electrode is normallybiased negative in relation to the cathode while control signals swingthe control electrode in the positive direction in relation to thecathode; means to apply cathode-anode space path voltage to the saidtube; and means responsive to the cathode-anode space path current ofthe tube.

5. A control mechanism responsive to a non-audible control signalinterposed on a main signal, the mechanism comprising in combination:means operable to separate the control signal from the main signal;integrating means responsive to the duration of the control signal; anelectron tube having cathode, anode and control electrodes; an operatingrelay having a winding and a pair of normally open contacts; a source ofunidirectional E. M. F.; means connecting said source to thecathode-anode space path of the tube through the relay winding; meansconnecting said integrating means to the control electrode of said tube,whereby control signal maintained for a predetermined period causes thetube to draw relay pickup current; means operable to supply apredetermined negative bias voltage to the control electrode of saidtube, said means having substantial resistance and normally maintainingthe space current in the tube to a predetermined value below relayactuating current; means including said normally open contactsconnecting the control electrode of said tube to a point of positivepotential, whereby the relay seals in the actuated condition; and meansselectively operable to reduce said point to a low potential to causethe relay to drop out.

6. A control mechanism responsive to a non-audible control signalinterposed on a main signal, the mechanism comprising in combination:means operable to separate the control signal from the main signal;integrating means responsiveto the duration of the control signal; anelectron tube having cathode, anode and control elec trodes; anoperating relay having a winding and a pair of normally open, contacts;a source of unidirectional E. M. F.; means connecting said source to thecathodeanode space path of the tube through the relay winding; meansconnecting said integrating means to the control electrode of said tube,whereby control signal maintained for a predetermined period causes thetube to draw relay pickup current; means operableto supply apredetermined negative bias voltage to the control electrode of saidtube, said means having substantial resistance and normally maintainingthe space current in the tube to a predetermined value below relayactuating current; means including a series resistance and said normallyopen contacts connecting the control electrode of said tube to a pointof positive potential, whereby the relay seals in the actuatedcondition; and means selectively operable to reduce the positivepotential at said point to zero, thereby providing voltage divideraction imparting negative bias to the control electrode of the tube andpositively causing the relay to drop out.

7. A reproducing device for an elongated record medium wherein arecorded control signal of predetermined duration arrests movement ofthe medium, the device including: means to reproduce signals from themedium as it travels thereover; electrical drive means having a pair ofterminals operable in response to predetermined unidirectional E. M. F.across said terminals to drive the medium in signal-reproducingmovements; means to supply said E. M. F. and operable in response toreproduction of the control signal to discontinue said E. M. F.; and, acapacitor connected across said terminal and of size to maintain themovement of the record medium for a sufiicient time after loss of saidE. M. F. to cause the full signal-bearing length of said medium totravel past the said first means so that subsequent reproduction fromthe medium is free of the control signal.

No references cited.

